Overview
ISO/TR 19498:2015 is an international technical report published by the International Organization for Standardization (ISO) under the scope of ophthalmic optics and instruments. This report specifies a standardized method for correlating a given set of optotypes with the established standard optotype-the Landolt ring-as defined in ISO 8596. The method ensures consistent visual acuity testing by comparing various optotype sets to the Landolt ring, which serves as the reference.
The standard outlines procedures for type testing optotypes and allows for suitable equivalent test methods to be substituted, providing flexibility while maintaining accuracy and comparability in visual acuity assessment.
Key Topics
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Correlation Methodology
ISO/TR 19498 details a rigorous approach to correlate new or alternative optotype sets with the standard Landolt ring. This involves selecting optotype sizes ranging from decimal acuity 2.0 to 0.4 in LogMAR steps of 0.1 to establish frequency of seeing curves.
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Test Environment Requirements
The test area is circular, with a diameter of 4° ± 1°, surrounded by a 15° ± 1.5° homogeneously illuminated field to avoid measurement influence. Maintaining a test background luminance of approximately 200 cd/m² ± 50 cd/m² is mandatory for both the Landolt ring and the tested optotypes to ensure consistency.
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Visual Acuity Testing Procedures
Testing involves 120 presentations per optotype size, randomly ordered, with exposure times of 3 seconds and 4-second intervals. Observers must be fully corrected to a visual acuity of 1.0 or better. The probability of guessing is accounted for with a defined value of 0.125, reflecting the eight different possible optotypes or directions.
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Data Analysis and Acuity Scoring
The frequency of seeing is corrected for guessing, utilizing a mathematical formula to derive an acuity score from the observer's responses. Frequency of seeing curves are plotted against logarithmic optotype sizes for both the Landolt ring and tested optotypes, enabling threshold acuity determination at 50% recognition.
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Assessment of Optotype Equivalence
Equivalence between two optotypes is assessed by comparing averaged threshold values across multiple observers. A difference greater than 0.05 log units indicates non-equivalence. Additional statistical tests involving sample standard deviations and z-scores determine the significance of observed differences against accepted significance levels (commonly 5%).
Applications
ISO/TR 19498:2015 has critical applications in the development, validation, and quality control of ophthalmic optical instruments and visual acuity testing charts:
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Clinical Vision Testing
Provides standardization for validating new optotypes used in diagnostic charts ensuring their reliability and comparability with the Landolt ring, widely accepted as a reference in visual acuity tests.
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Device and Diagnostic Manufacturing
Guides manufacturers of ophthalmic devices and vision-testing instruments in ensuring their optotypes meet international standards for accurate visual function assessment.
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Research & Development
Facilitates the design and testing of novel optotype sets for research, allowing proper correlation with the validated Landolt ring optotype for consistency in study subjects’ visual acuity measurements.
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Regulatory Compliance
Supports compliance with international standards for medical devices related to ophthalmic optics, ensuring harmonized and globally accepted vision testing protocols.
Related Standards
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ISO 8596:2009 – Ophthalmic optics - Visual acuity testing - Standard optotype and its presentation
This primary standard defines the Landolt ring optotype and prescribes procedures for visual acuity testing which ISO/TR 19498 builds upon for correlation methods.
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ISO/IEC Directives – Guidelines for preparation and maintenance of ISO standards and technical reports, underlining editorial and procedural consistency.
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ISO 14705 (if applicable) – Ophthalmic optics standards related to other types of vision charts or instruments may complement testing frameworks.
By adhering to ISO/TR 19498:2015, professionals in ophthalmology, optometry, and medical device manufacturing can ensure optotype sets used in visual acuity testing are reliably correlated with international benchmarks, delivering high-quality, consistent patient assessments globally.
